ORIGINAL ARTICLE

Bone strength index in adolescent girls: does physical activity make a difference?

D A Greene¹, G A Naughton¹, J N Briody², A Kemp³, H Woodhead⁴, L Corrigan⁵

¹ Centre of Physical Activity Across the Lifespan (CoPAAL), Australian Catholic University, Quakers Hill, NSW, Australia
² Department of Nuclear Medicine, The Children’s Hospital, Westmead, Australia
³ Department of Medical Imaging, The Children’s Hospital, Westmead
⁴ Department of Endocrinology, The Children’s Hospital, Westmead
⁵ Laurentian University, Sudbury, Ontario, Canada

Correspondence to:
Correspondence to:
Dr Greene
Australian Catholic University, Locked Bag 2002, Strathfield, NSW 2135, Australia; d.greene{at}mary.acu.edu.au

Background: Bone strength index (BSI) combines bone mineral and bone biomechanical properties to measure resistance to bending. This index may have greater clinical significance than the more often described markers of bone mineral content (BMC), areal density, or geometry alone and, in turn, may show a stronger relation to fracture risk. The BSI is the product of volumetric cortical bone mineral density (BMD) and cross sectional moment of inertia within a region of interest. Calculations combine dual energy x ray absorptiometry and magnetic resonance imaging technologies and provide a useful, non-invasive measure of in vivo bone strength.

Objectives: (a) To compare BSI in adolescent female middle distance runners and age matched controls; (b) to examine factors predictive of BSI in adolescent girls.

Methods: Twenty adolescent female middle distance runners (mean (SD) age 16 (1.7) years, physical activity 8.9 (2.1) hours a week) and 20 female controls (age 16 (1.8) years, physical activity 2.0 (0.07) hours a week) were recruited. To calculate BSI, a region of interest representing 10% of the mid-distal tibia was analysed for dual energy x ray absorptiometry derived BMC and was combined with bone geometry and biomechanical properties obtained by magnetic resonance imaging assessments. Potential predictors of BSI were also examined.

Results: Independent t tests showed that BMC (p = 0.028), cortical bone volume (p = 0.002), volumetric cortical BMD (p = 0.004), cross sectional moments of inertia (p = 0.005), and BSI (p = 0.002) were higher in the distal tibia of athletes than of controls. The strongest predictor of BSI was hours of physical activity a week (R² = 0.46).

Conclusions: Athletes habitually exposed to high training loads displayed greater BSI at the distal tibia than controls. The results further confirm BSI as a significant and discerning marker in musculoskeletal health in adolescent girls engaged in high and low mechanical loading.

Abbreviations: BMC, bone mineral content; BMD, bone mineral density; BSI, bone strength index; CSMI, cross sectional moment of inertia; CSA, cross sectional area; CV, coefficient of variation; DEXA, dual energy x ray absorptiometry; LTM, lean tissue mass; MRI, magnetic resonance imaging; ROI, region of interest

Keywords: adolescent girls; bone strength index; middle distance running; dual energy x ray absorptiometry; magnetic resonance imaging

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Commentary

M Karlsson⁶

⁶ Department of Orthopaedics, Malmö University Hospital, Lund University, SE-20502 Malmö, Sweden; magnus.karlsson{at}orto.mas.lu.se

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